Cooling Fan Module for a Motor Vehicle

ABSTRACT

A cooling fan module for a motor vehicle has a first fan motor which is used to drive a first cooling fan and a second fan motor which is used to drive a second cooling fan. A control unit ( 6, 13 ) is associated with the first fan motor ( 2, 11 ), which operates the first fan motor ( 2, 11 ) and the second fan motor ( 4, 12, 23 ) simultaneously, in order to provide an economical and compact technical solution for the cooling fan.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of International Application No. PCT/EP2006/066001 filed Sep. 5, 2006, which designates the United States of America, and claims priority to German application number 10 2005 048 886.2 filed Oct. 12, 2005, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a cooling fan module for a motor vehicle. In particular the invention relates to a cooling fan module with a first fan motor for driving a first cooling fan and with a second fan motor for driving a second cooling fan.

BACKGROUND

Frequently two or more cooling fans are used in cooling fan modules for motor vehicles. When two cooling fans are used the module is referred to as a double module. There are a number of reasons for using more than one cooling fan:

One is that the space available in the motor vehicle is often restricted. Another is that the fan output required is often an argument for using a number of cooling fans. Since for higher outputs the fan motors employed are of greater length it often makes sense, in respect of the length of module needed, to divide the module up into two smaller, shorter fan motors. If high cooling power is required, a separation into two (or more) cooling fans is often sensible and/or necessary, since, because of its inadequate heat removal, a single fan motor cannot provide the power needed.

In addition it can be necessary, because of the design of a motor vehicle or for other reasons, to use heat exchangers which have a more rectangular shape. By contrast with a cube shape, a double-fan configuration makes more sense for a rectangular shape, since a greater coverage of the heat exchanger can be achieved with this shape and the air flow from the corners of the heat exchanger is improved.

Finally two or more cooling fan modules can be used if—for example for reasons of availability—a redundancy is to be achieved.

Previously such double modules have featured two dc motors with brushgear which have been operated either in series or in parallel, in order to obtain specific speeds and thereby power output stages. In newer applications the dc motors with brushgear are operated with PWM controllers which are either internal, external or integrated into the two motors.

Increased demands in respect of module length, power and costs have also demanded new approaches to solutions for double modules.

SUMMARY

A cost-effective and compact fan cooling can be provided according to an embodiment by a cooling fan module for a motor vehicle, with a brushless first fan motor for driving a first cooling fan and with a second fan motor for driving a second cooling fan, with a control unit being assigned to the first fan motor, which, at the same time as operating the first fan motor, also operates the second fan motor.

According to a further embodiment, the first fan motor and the second fan motor may be connected in series. According to a further embodiment, the control unit may comprise a power supply independent of the power supply of the fan motors.

According to yet another embodiment, a method for operating a cooling fan module for a motor vehicle, with the cooling fan module having a brushless first fan motor for driving a first cooling fan and a second fan motor for driving a second cooling fan, with a control unit being assigned to the first fan motor, may comprise the steps of: operating the first fan motor as well as the second fan motor at the same time, and controlling the first fan motor via the control unit with speed regulation and the speed of the second fan motor being set as a function of the speed of the first fan motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described below with reference to an exemplary embodiment which is explained in greater detail with the aid of drawings. The drawings show the following simplified diagrams:

FIG. 1 a schematic block diagram of a serial double module and

FIG. 2 a switching diagram of a serial double module with a second motor with brushgear,

DETAILED DESCRIPTION

The cooling fan module according to various embodiments may have a brushless first fan motor for driving a first cooling fan and a second fan motor for driving of a second cooling fan, with the first fan motor being assigned a control unit, which operates the first fan motor at the same time as the second fan motor.

Such a cooling fan module allows a method to be implemented with which the first fan motor is activated with its speed regulated and the speed of the second fan motor is set as a function of the speed of the first fan motor.

A basic idea according to various embodiments is to provide a hybrid arrangement of a brushless fan motor with a second fan motor. In this arrangement only one electronic unit is used for the brushless fan motor and this is also used for the second fan motor. In other words the second fan motor (which does not have a control unit of its own) is operated automatically and inevitably as soon as the first fan motor is operated. Only a single control unit is employed in this case.

The solution according to various embodiments is thus a complete contrast with previously known approaches in which a single control unit can only be used to operate two fan motors because the control unit has two separate actuation units, namely one for each fan motor. Strictly speaking, such known control units consist of two individual control units which are accommodated in one and the same housing.

Because a brushless fan motor is used, considerably higher reliability and service life of the cooling fan can be achieved compared to conventional solutions.

The use of a brushless fan motor also makes it possible to implement a double or multiple fan configuration with a very short physical length. Despite a restricted length it is possible with this design to integrate the control unit into the brushless cooling fan. This is not possible without increasing the length with brushless dc motors as are used in conventional arrangements.

A higher system efficiency overall can be achieved since the brushless fan motor as a rule has an approximately 10-15% higher efficiency.

In accordance with one embodiment the first fan motor and the second fan motor may be connected in series, so that a “serial double module” is produced.

In accordance with one embodiment the control unit may be connected to a power supply line and a ground line and may have a number of connection elements for connecting the first fan motor. The control unit in such cases can be arranged on the one hand in the housing of the first fan motor. On the other hand however it can also be provided outside the housing of the first fan motor as an external control unit.

The first fan motor is preferably a brushless motor with any number of phases, for example with three or five phases, which is operated in bipolar or unipolar mode. The second fan motor preferably involves a brushless dc motor which is connected in series with the power supply line of the control unit. The use of a dc motor with brushgear enables the cooling fan module to be produced in a more cost-effective manner than comparable solutions with two brushless fan motors. Since no separate control unit has to be provided for the direct current motor with brushgear, none of the components listed below are needed either: Voltage regulator, microcontroller, resonators or similar, power components such as MOSFETs or diodes, driver stages, interface switching elements, etc. This reduces the manufacturing costs.

In addition the use of a dc motor with brushgear has further advantages: The interference suppression elements of the dc motor with brushgear as well as the inductance of the dc motor with brushgear itself operate as interference-suppression elements for the brushless drive. This enables the outlay for interference suppression (filters etc.) for the brushless drive to be reduced.

The speed of the first motor is regulated in accordance with a further embodiment in the control unit, which receives setpoint speed information as its input signal. It is also especially advantageous for the control unit to have a power supply independent of the power supply of the two fan motors.

According to various embodiments, a cooling fan module for a motor vehicle features a first fan motor 2 for driving a first cooling fan 3 and a second fan motor 4 for driving a second cooling fan 5. FIG. 1 shows such a double configuration in a greatly simplified illustration, in which the power supply line 9 as well as the further connecting lines are only shown schematically. The integrated control unit 6 of the first fan motor 2 serves as the sole control unit for simultaneous operation of the second fan motor which is connected in series with the first fan motor 2. The integrated control unit 6 in this case is arranged in the housing 7 of the first fan motor 2, while the housing 8 of the second fan motor remains free and can accordingly be designed smaller.

In an exemplary embodiment (cf. FIG. 2) a cooling fan motor for a motor vehicle has a brushless motor 11 as the first fan motor and a dc motor with brushgear 12 as the second fan motor. The cooling fans 3, 5 themselves are not shown in order to improve the clarity of FIG. 2. The fan motors 11, 12 are connected in series. The brushless motor 11 features an integrate control unit 13 while no separate control unit is required according to various embodiments for the dc motor with brushgear 12. In the exemplary embodiment shown the brushless motor 11 is a three-phase, bipolar-operated motor (ac motor).

The control unit 13 has control electronics 14, which for power supply of the fan motors 11, 12 with a supply voltage, is connected to a standard vehicle main power supply line 15 (“terminal 30”) of the motor vehicle and a corresponding ground line 16 (“terminal 31”). The fan motors 11, 12 are each designed in this case for a voltage which is far lower than the supply voltage, e.g. for half the supply voltage in each case. To control the brushless ac motor 11 with a three-phase ac system the control unit 13 is equipped in its power element with the functionality of a converter. An arrangement of electronic switching transistors 17, 17′ (power transistors, MOSFETs) is used for this, as is required for control of the brushless ac motor 11. Since the control unit 13 of the brushless ac motor 11 is also used for the operation of the dc motor with brushgear 12, it must be designed for both motor currents, i.e. in the design of the control unit 13 a corresponding power dissipation must be taken into account in the dimensioning.

For electrical power supply of the control electronics 14 independent of the supply voltage over the lines 15, 16 a separate normal vehicle auxiliary power line 18 (“terminal 15”) is provided. When power line 18 is switched off the no-load current draw of the control unit 13 is almost zero. In addition the control electronics 14 is connected via a connecting line 22 to an external signal generator (not shown) which provides setpoint speed information.

To connect the brushless ac motor 11 the control unit 13 has three phase connections 19 which are connected accordingly to the electronic switching transistors 17, 17′. The dc motor with brushgear 12 is connected in series to the direct current power supply line. The converter current, i.e. the total current through the plus-side switching transistors 17, flows through the dc motor with brushgear 12 and forms its current I. In a first approximation the power element of the control unit 13 thus acts as current source for the dc motor with brushgear 12. In other words the power element (converter) impresses a current into the power line and thus creates a corresponding torque in the dc motor with brushgear 12. The characteristic curve of the fan thus produces an associated constant speed of the dc motor with brushgear 12. An equally high current I also flows as total current through the brushless ac motor 11.

The connection of a dc motor with brushgear 12 to a brushless ac motor 11 for achieving the effect according to various embodiments is possible in a simple manner. To this end the dc motor with brushgear 12 must be connected into the power supply line 15 of the brushless ac motor 11. In addition a separate power supply for the control electronics 14 is needed, as is undertaken in the present example via the power supply line 18 (“terminal 15”).

The series circuit of the two fan motors 11, 12 has the following effects:

Since the voltage available for the power supply of the fan motors must be divided up, it is of advantage to select fan motors which have approximately the same power consumption. If for example a total output of 800 W is needed with a supply voltage of 12V, a brushless 400 W ac motor and a 400 W dc motor with brushgear are preferably used, with a motor voltage of 6V being available for each fan motor.

In the event of a polarity reversal of the supply voltage (power supply lines 15, 16) an automatic current limiting is produced by the dc motor with brushgear 12. The dc motor with brushgear 12 starts up in such cases.

By limiting the current in the brushless ac motor 11 with integrated control unit 13 the current is also limited in the dc motor with brushgear 12 without additional electronic components or other measures being necessary. If the supply voltage of the brushless ac motor is measured, under some circumstances a standstill (blocking) of the dc motor with brushgear can be detected, since then only the voltage drop at the internal resistance of the dc motor occurs, but no longer any counter EMF. Thus a significant voltage increase is measurable which leads to the deduction that there has been blocking. This enables both a blocking protection function and also a short-circuit protection function to be achieved in a simple manner for the direct current motor with brushgear 12.

A further advantage of the arrangement according to various embodiments is that no further electronic components are required for the dc motor with brushgear 12. Since the dc motor with brushgear 12 does not have a separate control unit, no power dissipation occurs through electronic components. This also reduces the cooling effort required.

The series connection according to various embodiments of the two fan motors 11, 12 also has effects on the operating behavior of the two cooling fans 3, 5. The brushless ac motor 11 is operated via the control unit 13 with speed regulation.

The fan law M=c*n2 means that a unique relationship between speed n and torque M is produced (c=fan constant). The torque M in its turn is proportional to the motor current I. Thus the speed-regulated brushless ac motor 11 represents a current source for the dc motor with brushgear 12. The impression of the current I into the direct current motor with brushgear 12 produces an impressed torque M as a result of the unique relationship between current I and torque M in the dc motor with brushgear 12. Through its cooling fans 5 and once again the fan law an associated speed n′ is once again produced. The relationship shown then applies in a similar fashion for the entire speed range. The precise relationship is left to the respective application and the layout of the fan motors 11, 12. With changes of load of the dc motor with brushgear 12 a self-limiting function occurs. If the load is reduced (e.g. by the wind generated when a vehicle is on the move), the speed n will be reduced by the impressed torque M. This however increases the counter EMF (electromotive force) and less supply voltage is available to the brushless ac motor 11. The result of this is that the speed regulation starts to limit the speed. This means however that a constant torque M is no longer impressed into the dc motor with brushgear 12. In the event of the load in the dc motor with brushgear 12 increasing, its speed is reduced. This reduces the counter EMF, which means that a higher voltage is available for the converter of the brushless ac motor 11. The converters can make adjustments and thereby keep the current I constant. The result, because of the impressed current, is that the current I through the dc motor with brushgear 12 is also constant. Overall both an increase in output and also and overload are safely prevented by the configuration according to various embodiments.

In summary, rather than the speed of a dc motor with brushgear 12 being regulated, its current is regulated.

This current regulation is undertaken indirectly according to various embodiments, since the current I (which also flows through the dc motor with brushgear 12) is set precisely as required by the cooling fan 3 of the brushless ac motor 11.

In a further exemplary embodiment (not shown) the inductance of the dc motors with brushgear 12 can be used not just as an interference suppression element, but also as a storage element of a boost converter. This enables an “intermediate network” with a higher voltage to be created with a comparatively low additional outlay in electronic components, which results in lower currents and thus also lower losses. The advantage of this solution with boost converter function lies in the fact that the two fan motors 11, 12 can be designed for higher voltages. This approach is mainly useful with outputs greater than 1 kW, e.g. with a brushless drive with 1000 W output and a drive with brushgear with 500 W output. 

1. A cooling fan module for a motor vehicle, with a brushless first fan motor for driving a first cooling fan and with a second fan motor for driving a second cooling fan with a control unit being assigned to the first fan motor, which, at the same time as operating the first fan motor, also operates the second fan motor.
 2. The cooling fan module according to claim 1, wherein the first fan motor and the second fan motor are connected in series.
 3. The cooling fan module according to claim 1, wherein the control unit comprises a power supply independent of the power supply of the fan motors.
 4. A method for operating a cooling fan module for a motor vehicle, with the cooling fan module having a brushless first fan motor for driving a first cooling fan and a second fan motor for driving a second cooling fan, with a control unit being assigned to the first fan motor, the method comprising the steps of operating the first fan motor as well the second fan motor at the same time, and controlling the first fan motor via the control unit with speed regulation and the speed of the second fan motor being set as a function of the speed of the first fan motor.
 5. The method according to claim 4, wherein the first fan motor and the second fan motor are connected in series.
 6. The method according to claim 4, wherein the control unit comprises a power supply independent of the power supply of the fan motors.
 7. A cooling fan module for a motor vehicle, with a brushless first fan motor for driving a first cooling fan and with a second fan motor for driving a second cooling fan, with a control unit being assigned to the first fan motor, which, at the same time as operating the first fan motor, also operates the second fan motor, wherein the control unit is operable to control the first fan motor with speed regulation and the speed of the second fan motor being set as a function of the speed of the first fan motor.
 8. The cooling fan module according to claim 7, wherein the first fan motor and the second fan motor are connected in series.
 9. The cooling fan module according to claim 7, wherein the control unit comprises a power supply independent of the power supply of the fan motors. 